1. Field of the Invention
The present invention relates to an infrared radiator, and more particularly, an infrared radiator embodied as a surface radiator.
2. Description of the Related Art
Infrared radiators embodied as surface radiators are used in dryer systems which are used to dry web materials, for example, paper or board webs. Depending on the width of the web to be dried and the desired heating output, the requisite number of radiators is assembled with aligned emission surfaces to form a drying unit.
The basic structure of a single generic infrared radiator is illustrated in FIG. 8 and described, for example, in DE 199 01 145-A1.
The fuel/air mixture needed for the operation of the radiator is supplied to the radiator through an opening (a) in the housing (b) and firstly passes into a distribution chamber (c), in which the mixture is distributed uniformly over the radiator surface, at right angles to the view shown here. The gases then pass through a barrier (d) which is configured so as to be permeable. The main task of the barrier (d) is to isolate the combustion chamber (e), in which the gas is burned, from the distribution chamber (c), in which the unburned gas mixture is located, in such a way that no flashback from the combustion chamber (e) to the distribution chamber (c) can take place. In addition, the barrier (d) should expediently be designed such that the best possible heat transfer from the hot combustion waste gases to the solid element that emits the radiation, that is to say the surface of the barrier (d) itself or possibly the walls of the combustion chamber (e) and the actual radiant element (f) is prepared.
The geometric/constructional configuration of combustion chamber (e) and radiant element (f) is likewise carried out from the following points of view:    optimized heat transfer,    maximized heat emission,    minimum heat losses to the side and in the direction of the distribution chamber, taking into account thermal expansion which occurs and application specific special features, such as possible contamination, thermal shock which occurs, and so on.
U.S. Pat. No. 3,751,213 discloses a further generic infrared radiator, in which the radiant element includes a honeycomb element with continuous holes to carry the combustion gases away. The barrier (“gas injection block”) is designed as a perforated ceramic plate. The main advantage described in the patent specification of the honeycomb element consists in the fact that the holes contained therein act as black radiators if their length/diameter ratio exceeds the value 5.
When assembling individual radiators to form drying units, these are normally ignited from the front through the radiant element. For this purpose, the openings in the radiant element must have a certain minimum area in order to ensure speedy thorough ignition of the gas operated infrared radiator of the drying unit. In the case of circular cross-sections, the minimum diameter is around 4 mm. This requirement, given the predefined length/diameter ratio, results in a minimum height of the honeycomb structure of 20 mm and therefore a comparatively large mass to be heated up. The relatively large openings in the radiant element, which are necessary in order to ignite the radiator, lead to relatively low gas velocities and therefore to a comparatively poor convective heat transfer from the combustion waste gases to the radiant element. Furthermore, no material is known at present which permits the construction of a barrier in the form described in U.S. Pat. No. 3,751,213 and at the same time withstands the very high combustion chamber temperatures typical of this construction for a relatively long time.
What is needed in the art is an infrared radiator which has an improved convective heat transfer with high service life.